WASHINGTON 
John Sweeney spent the past 14 years building the AFL-CIO into a political powerhouse for worker's rights and other progressive Democratic causes.

Yet over the same time, the ranks of union members continued to shrink, diminishing organized labor's clout in the workplace. Frustration with Sweeney's tenure and the dip in membership led seven unions to split from the AFL-CIO four years ago to form the rival Change to Win federation.

As Sweeney, 75, prepares to step down next week as AFL-CIO president, his successor and longtime deputy – Richard Trumka – wants to aggressively recruit younger workers and boost membership as a means of expanding labor's political influence.

Trumka, 60, officially takes the helm of the AFL-CIO at its quadrennial convention, which opens Sunday in Pittsburgh. On Tuesday, President Barack Obama addresses the nation's largest labor federation, which represents about 11 million workers in 56 unions.

By many accounts, Sweeney transformed a moribund labor movement in the mid-1990s by firmly aligning the AFL-CIO with the Democratic left. The son of working class Irish immigrants from the Bronx repositioned the AFL-CIO as a champion of social Democratic causes by forging alliances with civil rights leaders, women's groups, environmental and anti-poverty groups.

Besides giving the federation more political heft, he mobilized rank-and-file union members to boost political activism, beef up voter registration drives and expand get-out-the-vote efforts. Sweeney also started Working America, an AFL-CIO affiliate for people who don't have a union at work, that now boasts 3 million members.

"He turned to these new models of organizing the base as a way to gain political power," said Dorothy Sue Cobble, professor of history and labor studies at Rutgers University in New Brunswick, N.J.

Making political action a year-round affair, rather than just focusing on elections, allowed the AFL-CIO to mobilize quickly this summer to help Obama push his health care overhaul. Last month, 24,000-plus union members showed up at more than 400 town hall meetings and rallies in all 50 states to counter those who oppose Obama's ideas for changing health care.

But Sweeney could not seem to find the answer to steep membership declines. Union membership now stands at about 12.4 percent, down from a high of 35 percent in the 1950s. The drop has been steeper in the private sector, which has shrunk to 7.6 percent from about 17 percent in the 1980s.

At the AFL-CIO's 2004 convention in Chicago, several of the federation's largest unions resigned. Led by Service Employees International Union president Andy Stern, the leaders complained there was not enough emphasis on organizing and too much emphasis on politics.

"There's no question about it, the disaffiliation was very hard," Sweeney said in an interview. "We really can't afford to be split."

While the AFL-CIO took a major financial hit from lost dues, union leaders say the split was felt more at the top than at the lower ranks, where most local unions continued to affiliate with the old federation.

The impact at the new Change to Win federation was less dramatic than expected. SEIU and the Teamsters have seen modest growth, but other unions have not done as well. And the newer federation has continued to spend heavily on political efforts too.